/*

  * #%L

  * StringEncoder.java - mongodb-async-driver - Allanbank Consulting, Inc.

  * %%

  * Copyright (C) 2011 - 2014 Allanbank Consulting, Inc.

  * %%

  * Licensed under the Apache License, Version 2.0 (the "License");

  * you may not use this file except in compliance with the License.

  * You may obtain a copy of the License at

  * 

  *      http://www.apache.org/licenses/LICENSE-2.0

  * 

  * Unless required by applicable law or agreed to in writing, software

  * distributed under the License is distributed on an "AS IS" BASIS,

  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

  * See the License for the specific language governing permissions and

  * limitations under the License.

  * #L%

  */

 package com.allanbank.mongodb.bson.io;

 import java.util.Collections;

 import java.util.HashMap;

 import java.util.List;

 import java.util.Map;

 import java.util.SortedMap;

 /**

  * StringEncoderCache provides the ability to cache the encoding of a string to

  * speed the writing of strings.

  * <p>

  * This class is thread safe. Thread safety is achieved by maintaining two data

  * structures. The first is a map of seen strings to the number of times the

  * string has been seen. The map is maintained by the base class:

  * {@link AbstractStringCache}. The second structure is a simple map of the

  * cached {@link String} to the encoded {@code byte[]}. The map has no locking

  * or synchronization since it is read-only after construction.

  * </p>

  * 

  * @api.no This class is <b>NOT</b> part of the drivers API. This class may be

  *         mutated in incompatible ways between any two releases of the driver.

  * @copyright 2014, Allanbank Consulting, Inc., All Rights Reserved

  */

 public class StringEncoderCache extends AbstractStringCache {

     /** The cache of strings to bytes. */

     private Map<String, byte[]> myCache;

     /**

      * Creates a new StringEncoder.

      */

     public StringEncoderCache() {

         myCache = Collections.emptyMap();

         myMaxCacheLength = DEFAULT_MAX_CACHE_LENGTH;

         myMaxCachEntries = DEFAULT_MAX_CACHE_ENTRIES;

     }

     /**

      * Looks in the cache for encoded bytes for the specified string.

      * 

      * @param string

      *            The string value to find the cached bytes for.

      * @return The cached bytes for the string. May be <code>null</code>.

      */

     public byte[] find(final String string) {

         return myCache.get(string);

     }

     /**

      * Clears the cache.

      */

     @Override

     protected void clear() {

         myCache = Collections.emptyMap();

         super.clear();

     }

     /**

      * Rebuilds the cache from the current collection of seen entries.

      */

     @Override

     protected void rebuildCache() {

         final SortedMap<Integer, List<SeenString>> order = buildCacheGroups();

         // Rebuild the cache.

         int count = 0;

         final Map<String, byte[]> cache = new HashMap<String, byte[]>(

                 (int) Math.ceil(Math.min(order.size(), myMaxCachEntries) / 0.75));

         for (final List<SeenString> seenAtCount : order.values()) {

             for (final SeenString seen : seenAtCount) {

                 if (count < myMaxCachEntries) {

                     cache.put(seen.getValue(), seen.getBytes());

                     count += 1;

                 }

                 else {

                     mySeen.remove(seen.getValue());

                 }

             }

         }

         myCache = cache;

     }

 }